The prior art comprises the use of air and/or oxygen biological reactors and is explained in detail below with an example and with reference to FIG. 1 in which:
E=entry of the water to be depurated, PA1 N=neutralization tank, PA1 CH=dosage of neutralization products, PA1 V1=homogenization tank PA1 V2=biological reaction tank, PA1 V3=sludge decantering tank, PA1 A=input of air or O.sub.2 PA1 RF=sludge recycling, and PA1 FS=waste sludges. PA1 1--With compressed air or oxygen input through porous plates or pipes uniformly distributed on the bottom of the tanks V1 and V2; PA1 2--With air or oxygen sucked in by a Venturi tube effect by pumps fitted with nozzles distributed in some points on the bottom of tanks V1 and V2; PA1 3--With rotors set at the free surface of tanks V1 and V2 that raise the water and spray it into the surrounding air aerating it as it falls. PA1 at least three tanks are required in order to obtain neutralization also by means of chemical products; PA1 it is necessary to add compressed air or oxygen to the water by means of porous plates or pipes, with a variable porosity, for instance between 30.mu. and 250.mu., that consequently generate micro-bubbles that expand reducing the gas-water contact surface, that is already scarce with the above porosity values. PA1 administration by means of a few Venturi type nozzles, with large diameter water spouts, e.g. 40-80 mm., and with water pressure around 1.5-2 Kg/cm.sup.2 does not enhance the dimensions of the air-water contact surfaces, because the same spout is not in a cavitation condition. PA1 the air and oxygen, inside the ejector, are dragged and not intimately mixed into the water as would be desirable. PA1 the water is raised by 1 or 2 meters with a centrifuge blade wheel and launched into the surrounding air; also in this case there are no relevant air-water contact surfaces are generated, given the scarce energy in breaking the surface tension (cavitation). PA1 in none of the three cases for administration described above there is contemporary separation phenomenon by sludge flotation, but only re-mixing appears. PA1 the roughness and limited dimensions of the air-water contact surfaces in the three methods described above do not lead to any useful natural correction of the pH and appreciable reduction of toxicity, owing to the presence of inorganic reduction substances (chemical reactions due to sufficient molecular dissolution of the oxygen). PA1 the treatment of the waters produces waste sludges (FS). PA1 the time of permanence in the homogenization and biological reaction tanks are practically limited to the value of the ratio between the volume of said two tanks and the hourly delivery of water to be depurated. PA1 while with the current technique the different functions are physically separated and take place in more than one tank, with the invention they all take place in a single compact structure, thus requiring significantly more limited space availability, PA1 the re-circulation of all the liquid mass through the oxygenizers, operated by a pump which re-circulates each hour a water volume multiple of the one entroduced each hour into the tank dependion on the pollution extent of the water under treatement, increases the air-water contact time, contact time which is expressed as a ratio between the volume of the tank and the hourly delivery, in m.sup.3 /h of the waste water to be treated, according to the following formula: EQU t=(R/E)(V/E)+(V/E) in which: PA1 t is the contact time in hours, PA1 R is the pump hourly delivery rate, PA1 E is the polluted water hourly delivery in m.sup.3 /h, and PA1 V is the volume of the tank in m.sup.3. PA1 in the case of a tank equipped with air compressors and porous plates the value t is simply equal to V/E=24 hours; that is to say that the invention, in the example considered, leads to values of contact time three times higher than usual (24 hours) in the prior art. PA1 the distribution of the oxygenizers, in opposition upon their plane and the circulation of the waste water induced by their thrust, causes the micro-diffuision of the oxygen in the air to be uniform throughout the mass, as it is sucked in and in a state of liquid cavitation within the same oxygenizers. This micro-diffusion not only supports the biological reactions in the reaction zone (stage V.sub.2 of the prior art), but also activates the oxide-reduction and the natural neutralization reactions both within the oxygenizers, and in the same reaction and flotation region (stage N and CH in the prior art); moreover it enhances the separation by flotation towards the reaction and flotation region also of particles in colloidal state (concentrator of sludges and foams in zone H, extractor of gaseous ammonia and volatile substances).
The administration of air or oxygen takes place in one of the following ways:
The drawbacks of the prior art are shown below: